[erlang-questions] Differentiating between FQDN and IP addresses
Sachin Joshi
zxq9
> I am getting an input in a program as 'ip address' or 'FQDN'. I need to
> identify if it is an ipv4 or ipv6 or a hostname(fqdn).
> Can someone help me in this?
Hi, Sachin.
I'm assuming you are receiving these as strings.
The function inet:parse_strict_address/1 can help you determine if the string is a valid IPv4, IPv6, or invalid IP address.
http://erlang.org/doc/man/inet.html#parse_strict_address-1
If it is an invalid IP address, then attempt to use it as a FQDN instead. If that fails, then perhaps it is invalid in general.
As for "what is a valid FQDN?" the standard has slid a lot in recent years, so it seems more common to just try it out (perhaps converting a utf-8 string via punycode first to see if that fails) and see if it barfs or not.
Imagine something along the lines of...
> -spec interpret_address(string()) -> Result
> when Result :: {ipv4, inet:ipv4_address()}
> | {ipv6, inet:ipv6_address()}
> | {fqdn, inet:hostname()}.
>
> interpret_address(String) ->
> case inet:parse_strict_address(String) of
> {A, B, C, D} ->
> {ipv4, {A, B, C, D}};
> {A, B, C, D, E, F, G, H} ->
> {ipv6, {A, B, C, D, E, F, G, H}};
> {error, einval} ->
> {fqdn, String}
> end.
With the exception that the result on {error, einval} should really look like:
> {error, einval} ->
> validate_fqdn(String)
and the overall function should be allowed to return the type
> Result :: {ipv4, inet:ipv4_address()}
> | {ipv6, inet:ipv6_address()}
> | {fqdn, inet:hostname()}
> | {error, bad_address}.
But you can get the effect of this by just trying the return value of {fqdn, String} and see if it can actually resolve a hostname this way.
Or something like that.
Forgive my imprecision -- it is very late here. Hopefully this points you in the right direction.
-Craig
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